Recently, functions of portable terminal devices such as cell phones have become more diverse. For example, portable terminal devices that have an e-mail sending/receiving function and an internet connection function are widely prevalent. Users of the portable terminal devices frequently use these functions and in doing so they use a touch panel (hereinafter also referred to as a soft key) or hard keys to input characters.
As examples of the portable terminal devices, those with only a soft key and without hard keys and those with hard keys composed of alphabetic, keys (Qwerty keys) and a soft key are well known. In the portable terminal devices without hard keys, users input characters only by a soft key, which may cause more inputting errors and put a burden on the users.
Meanwhile, although in the portable terminal devices with Qwerty keys, since users input characters with both hands, the speed of character input tends to be faster, one-hand character input using a thumb, which is the most common among character input operations of cell phones and the like, cannot be performed.
Patent Literature 1 describes a cell phone having a slide structure in which a front side unit and a back side unit are coupled by slide engaging means. It describes the art that this cell phone has a plurality of stages of slide locking positions and a touch panel function of a display unit is controlled depending on each of the positions in order to increase its usability. FIG. 7 and paragraph [0072] of the Patent Literature 1 describe that touch panel control means controls a touch panel such that each portion of the touch panel is separately controlled to be enabled or disabled depending on each of the slide locking positions.    Patent Literature 1: Unexamined Japanese Patent Application KOKAI Publication No. 2003-179678